Coal-water slurries are well known to those skilled in the art. Some of them have a high solids content and can be burned directly without being dewatered. Some of them have a low viscosity and can be readily pumped through pipelines. Some of them are stable and can be stored for long periods of time in a quiescent state before being burned.
There are no prior art coal water slurries known to applicant which combine the properties of high solids content, low viscosity, and stability. The prior art teaches that high density coal-water slurries have high viscosities and are substantially unpumpable. Thus, as is taught in U.S. Pat. No. 4,104,035 of Cole et al., "As the solids content increases above this range the slurry becomes increasingly difficult to pump and at about 50% solids content it is unpumpable" (lines 30-33 of Column 1).
It would be advantageous for a coal-water slurry to possess the properties of stability, low viscosity, and a high solids content. Furthermore, the viscosity of this slurry should decrease at a constant shear rate; a slurry which possessed this property would become easier to pump as it was traveling through a pipeline of substantially constant diameter. Furthermore, the viscosity of this slurry should decrease at increasing shear rate; a slurry which possessed this property would, as, e.g., the diameter of the pipeline decreased, become easier to pump. Furthermore, because it is desirable to heat a coal-water slurry while it is being pumped to a furnace in order to facilitate its atomization, this slurry should have a negative temperature coefficient of viscosity.
It is an object of this invention to provide a deashed coal-water slurry which has a high solids content, has low viscosity, is stable, has a viscosity which decreases at a constant shear rate, at an increasing shear rate, or with increasing temperature, is cleaner and less viscous than comparable prior art coal-water slurries and which can be prepared without creating a substantial amount of waste fines. It is another object of this invention to provide a process for grinding such a slurry, for pumping such a slurry, and for cleaning a coal-water mixture to produce such a deashed slurry.